Drove down to London, and was at my mum's house loading some stuff into it - locked it and unlocked it a few times as I brought stuff out to the car in dribs and drabs. When I got the last lot of stuff, and was about to head back up the M40, I couldn't unlock the car. No response...dead!!!!

I thought the battery in the fob had gone, so I found/bought some new batteries and tried at least 3 - nothing. No response from the car at all. No lights flashing, no doors unlocking!!

So as I had to get back to Warwick in the same evening, I resorted to calling the AA, who were there in 10 minutes. We used the key blade to open thecar, which immediately set the alarm off. Somehow, it stopped again, and the AA guy checked the car battery. He suggested it was knackered, so I paid for a new one, which he had and fitted there and then. And hey presto - key fob working again and doors locking and unlocking. Well I never.....and I thought the fob circuit board or swtches might be broken??!!!

There are a couple of things that you need to be aware of if you change the battery in a fob, is that the key may (but not always) need synchronising before the remote will work again. This is done by putting the key in the ignition hole. But if you have locked the car, you need to use the passenger door to get in. Which you can't if you park against a wall...

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Guy did some checks on the car battery, and then put a booster on it, and we got the car started. He did more checks with voltmeter etc on the battery, and diagnosed the car battery was at fault (age unknown as it was in the car when I bought it, but it was a Halfords battery).

Once he'd changed it for a new battery (Bosch, 5 year warranty blah blah), we could unlock and lock the car again and all was OK once more. It was 8pm, Halfords was closed, and I needed to get back up the M40, so was just glad I was able to get back into the car.

I had literally been in and out of the car loading stuff in about 5 or 6 times, locking and unlocking the car each time when I went back into the house for more stuff. Then the last time I came out, pressing remote buttons did nothing.......

I obviously didn't have the second fob with me to try, but I was concerned perhaps the circuit board or the button contacts etc were worn out.

You say that, but I ordered the bigger battery for my 9-3 B207R Auto as I didn't check it properly.... It took over an hour to change as it meant removing the battery box and trying to undo the captive nut that lets you change between the bigger and smaller size of battery which eventually required some careful usage of the dremel. When I double checked the build spec for my car it had indeed been supplied from the factory with the 60aH battery.

He fitted a BOSCH S4004 BATTERY 075, which was the same physical size as the Halfords battery that was in the car already. In all the paperwork the previous owner gave me, I don't recall a receipt for a battery....so it could have been 7/8 years old or more.

I need to check the number on the battery, because there seem to be different ones with the same number. Some heavy duty, some 60aH, some higher......

My aero came fitted with 096 out of the factory..Bosch S4 004,i had a bigger battery fitted to my cavalier in 80/90's..With all the electrics in these cars do you really want a little weedy battery like the AA have fitted..

My main concern was that the car may not have needed a new 12V battery, just a new battery in the fob, and syncing to the car again as Will suggested. If that is the case, I've shelled out when all I needed to do was spend a quid on the fob battery.

I've been a member of the AA for all the years I have been driving, and only used them a handful of times in that time (been generally lucky with all the cars I've had), so if I've been conned, there will be a complaint going in. Then again, I have no way of proving anything as I don't have the old battery any more

You described the classic battery failure for a 9-3, I would be very surprised if it wasn't a battery failure. They tend to just die without warning which is why after a couple of false starts on mine last year I just replaced it, if there is ever any doubt it almost certainly is a battery problem.

I would also suggest that you keep 2 spare fob batteries in the glove box, I've done this for every car I've owned with a remote since I first got a car with remote locking 20 years ago (almost as long as I've been driving!) and know the procedure on how to replace them.

Oh well, that makes me feel a bit better..... I've been suspicious, but then again, that battery in the car was an aftermarket Halfords one and I couldn't see any date on it...and I don't have any receipts in amongst the paperwork I got from the previous owner which dates back to 2012, so it could have been a 7 year old aftermarket battery...…. in which case, it probably was ready to go.....